Medical linear accelerators (LINACs) are useful in producing high energy radiation to treat patients with cancer. Depending on the type of cancer, position, size of the tumor and its surrounding critical organs, and the patient size, medical LINACs operating at energies from ˜4 to ˜20 MeV range are used for radiation therapy procedures. To ensure safety however, protective measures must be taken to limit unwanted radiation to patients outside the planned treatment field and to radiotherapists and the general public to an acceptable level. Electronic components sensitive to radiation exposure in the system also need to be protected from excessive radiation to prolong their useful life span.
Radiation in directions other than the direction toward the intended places, such as tumor, is undesirable. Hence proper shielding is required. Unwanted radiation is called radiation leakage which in general have three major aspects: (1) Leakage to patients. This results in higher risk of patients getting secondary cancers, hence the lower the better. (2) Leakage to general public. Linac leakage to the operators or others is shielded by the treatment room. Reduced leakage can result in lower cost of the treatment room. (3) Leakage to the linac system itself. There are many PCBs and components located inside the treatment room and many of their performance degrade over time due to radiation damage. Reduced leakage to these parts can reduce the maintenance resource and service cost. Because of above, a well-designed shielded system is very important. Conventionally, machine shielding is developed based on a trial-and-error approach, which requires costly schedules, budgets and resources, and results in heavy and costly shielding parts and assembly. Furthermore, machine leakage performances are unknown until prototypes are constructed and actual measurements are made. In addition, unintended leakage hot spots may exist, incurring more expensive room shielding and short life span of electronic machine components. This application describes a systematic method to design and optimize the shielding that reduces the cost of the shielding itself and overall cost in above aspects.